1. Field of the Invention
The present invention relates to a pulsimeter for analyzing a pulse wave signal detected from the human body.
2. Description of the Related Art
FIG. 18 is a block diagram of the functions of a pulsimeter according to related technology as described in Japan Unexamined Patent Publication 7-227383.
As shown in FIG. 18, a pulse wave detection means 1801 detects a pulse wave signal from the body of a person or user using the pulsimeter, and outputs the detected signal to a frequency analyzer 1803. A body movement detection means 1802 detects movement of the body, and likewise outputs the detected signal to the frequency analyzer 1803. Frequency analyzer 1803 then analyzes the frequency of output signals from pulse wave detector 1801 and body movement detector 1802 using, by way of example only, a fast Fourier transform operation. A pulse wave component extractor 1804 identifies a pulse wave component equivalent to the frequency of the pulse based on the result of frequency analysis of the outputs from pulse wave detection means 1801 and body movement detection means 1802, and then outputs the extracted pulse wave component to a pulse rate calculator 1805. Pulse rate calculator 1805 calculates the pulse rate per minute using the frequency component of the pulse identified by pulse wave component extraction means 1804. A display 1806 then displays the pulse rate calculated by pulse rate calculator 1805.
Note that, as described above, a pulse wave component corresponding to the pulse frequency is extracted from the result of analyzing the frequency analyzing of a detected pulse wave signal and a body movement signal, and the pulse rate per minute is then calculated from the frequency component of the pulse. Both the pulse wave signal and body movement signal are required by the apparatus described above to determine the pulse wave component.
This is described more specifically below with reference to FIGS. 19A, B and C which shows the results of a fast Fourier transform of the pulse and body movement signals obtained from a subject when walking and running, two types of exercise having a different periodic characteristic. FIG. 19A shows pulse spectrum fmg, FIG. 19B shows movement spectrum fsg, and FIG. 19C shows the extracted pulse wave component fM, i.e., the spectrum obtained by subtracting the movement spectrum fsg from the pulse spectrum fmg. As shown by these figures, the pulse spectrum fmg 19A obtained from pulse wave detector means 1801 contains both the frequency component of the pulse wave form, and the frequency component of the signal resulting from body movement. Body movement detector 1802, however, reacts only to body movement, and the detection signal output therefrom thus contains only the frequency component of the signal resulting from body movement. The movement spectrum fsg is therefore removed from the pulse spectrum fmg, and the highest remaining value in line spectrum fM is used as the frequency component of the pulse. The pulse rate is then calculated based on the frequency component of this pulse wave signal.
The results of applying a fast Fourier transform to pulse wave signals and body movement signals detected while doing aerobics, playing tennis, and other types of exercise characterized by irregular movement are shown in FIGS. 20A, B and C. FIG. 20A shows pulse spectrum fmg, FIG. 20B shows movement spectrum fsg, and FIG. 20C shows the extracted pulse wave component fM, i.e., the spectrum obtained by removing the movement spectrum fsg from the pulse spectrum fmg.
As shown in FIGS. 19A-C the period of a signal representing exercise characterized by regular periodic motion has a specific line spectrum. When the exercise is not characterized by such regular motion, however, the body movement signal does not have a readily discernible periodic component, resulting in plural line spectrums. As a result, a plurality of line spectrums remains (FIG. 20C) even after the movement spectrum fsg is subtracted from the pulse spectrum fmg, and it is therefore not easy to identify the pulse wave frequency component.
A problem with a Fourier transform using a sine wave or other periodic signal as the basis function is that frequency analysis of local signal changes, i.e., analysis with high temporal resolution, is not possible. It is therefore not possible to extract a pulse wave component from a pulse wave signal with a superposed body movement component resulting from exercise characterized by irregular movement. This problem arises because the basis function is spread uniformly.